Coated refractory composition and method for making the same

Abstract

A composition comprising an alpha alumina substrate having a first coating layer of calcium pyrophosphate and a second coating layer of hydrous alumina, and to a calcined composition comprising an alpha alumina substrate having a first coating layer of calcium pyrophosphate and a second coating layer of a densified anhydrous, crystalline form of alumina and to a method for preparing the same.

What is claimed: 
     
       1. A composition comprising an alumina coated refractory ceramic particulate substrate of average particle size in the range of from 0.1 to 2500 microns having a first coating of a calcium component and a second coating of an alumina component, wherein said first and second coating comprises about 0.5 to 25 wt% of the total composition and the ratio of first coating to second coating is about 0.01 to 0.95. 
     
     
       2. The composition of claim 1 wherein the refractory substrate is alpha alumina. 
     
     
       3. The composition of claim 1 wherein the refractory substrate is selected from the group consisting of oxides, carbides, borides, nitrides of aluminum, titanium, zirconium, silicon and mixtures thereof wherein said refractory substrate surface is covered with a crystalline form of alumina. 
     
     
       4. The composition of claim 1 wherein the first coating is selected from the group consisting of calcium pyrophosphate, calcium phosphate, calcium silicate, calcium aluminate and mixtures thereof. 
     
     
       5. The composition of claim 1 wherein the second coating is hydrous alumina. 
     
     
       6. The composition of claim 5 wherein the hydrous alumina is predominately boehmite alumina. 
     
     
       7. A composition comprising an alpha alumina platelet having an average size in the range of from 0.1 to 2500 microns and a total composition surface area in the range of from about 17.3 to about 57.2 m 2  /g, said alpha alumina platelet having deposited thereon a first coating of calcium pyrophosphate and a second coating of boehmite alumina; wherein said first and second coating comprises 0.5 to 25 wt% of the total composition. 
     
     
       8. A composition comprising an alumina coated refractory particulate substrate of average particle size of 0.1 to 2500 microns having a first coating of a calcium component and a second coating of an alumina component wherein said first and second coatings comprise 0.5 to 25 wt% of the total composition and combine to provide a debonding function between a preform and a ceramic matrix. 
     
     
       9. A calcined composition comprising an alpha alumina substrate of average particle size of 0.1 to 2500 microns having a first coating of calcium pyrophosphate and a second coating of a densified, anhydrous, crystalline alumina coating wherein said first and second coatings comprise 0.5 to 25 wt% of the total composition.